Coiled steel tubing finds a number of uses in oil well operations. For example, it is used with wireline cable for running well tools, such as logging tools and perforating tools downhole. Such tubing is also used in the workover of wells, to deliver various chemicals and perform other functions or in any number of operations where coiled tubing may be remotely positioned such as in downhole production tubing, pipelines or flowlines.
In all operations, the various depth or distance measurements of a tool or some location on the coiled tubing in a remote location is important. Typically, the length of coiled tubing is measured by a wheel and mechanical counter as it is spooled off or onto the reel. The accuracy of such measuring devices is questionable particularly if long lengths of coiled tubing are deployed and retrieved from the well. The depths at which coiled tubing is used is expected to get substantially greater with the development of better materials and techniques. Thus, coiled tubing technology will need a commensurate development in depth measuring technology. Outside of the coiled tubing technology, techniques have been developed for electronically measuring the depth of drill pipe and casing.
Composite coiled tubing will likely be subject to much greater length variation as it is used, than is the case with steel tubing. Thus, for oil field applications, where precise positioning of tools, equipment, or the like on the tubing will be involved, the elongation of the composite coiled tubing string in use presents a location measurement problem more complex than normally encountered with steel coiled tubing.
Accordingly it is an object of the present invention to provide a new and improved system for position and depth measurement of downhole equipment in a wellbore using composite coiled tubing having integral and detectable indicia which are arranged along the length of the coiled tubing in a manner to permit the determination of the depth or position of the composite coiled tubing in the borehole.